The present invention relates to a process for producing ethylene-.alpha.-olefin copolymer rubbers.
It is already known to copolymerize ethylene and an .alpha.-olefin, or ethylene, an .alpha.-olefin and a non-conjugated diene compound by using a so-called Ziegler catalyst comprising a vanadium compound and an organoaluminum compound. It is also known to prepare a vanadium compound containing an alkoxy group by reacting a vanadium compound and an alcohol. As to a concrete method of using a vanadium compound containing an alkoxy group for polymerization, there is known a process which comprises separately feeding a vanadium compound and an alcohol into an inert hydrocarbon solvent containing an organoaluminum compound in a polymerization vessel, followed by mixing, to use for polymerization. This process, however, has a problem of greatly lowering the polymerization activity of the catalyst. In another known method, an inert hydrocarbon solution containing a vanadium compound and an inert hydrocarbon solution containing an alcohol are mixed beforehand in a batch type mixing vessel and the resulting solution is fed into an inert hydrocarbon solution containing an organoaluminum compound, to be used for polymerization. This method, however, has a problem in that the by-product of the reaction of the vanadium compound and the alcohol deposits in the mixing vessel as a precipitate and catalytic activity is lowered. As a method for solving such problems, JP-B-49-14542 discloses a process wherein the side reaction is suppressed by bubbling an inert gas such as nitrogen through the mixed solution containing a vanadium compound and an alcohol and thereby removing the protonic acid present in the solution. In such a process, which requires additional operation steps, however, neutralization treatment of a gas containing a large amount of corrosive substances is necessary and further, since a part of the inert hydrocarbon solvent is vaporized off, an environmental problem relating to air pollution takes place and the concentration of the catalyst fluctuates, which necessitates readjustment of the catalyst concentration to the intended level. Thus, this process is disadvantageous from the viewpoint of industrial operation.